Although the invention can be used advantageously in various cases in which an adsorbable and/or condensable component of a gas flow is to be removed from said flow, or the concentration of the component in the gas flow is to at least be reduced, the invention and the problem addressed thereby are to be explained in greater detail below by way of example on the basis of drying compressed air, in other words, reducing the water concentration in the compressed air. It is understood that a similar problem can also occur when dehumidifying other gases, in particular other pressurised gases, such as nitrogen, natural gas, or gases from chemical production processes.
An adsorption drying device for drying an in particular compressed gas, in which the adsorption material is located in a rotating adsorption chamber, and an adsorption drying method, in conjunction with which said adsorption drying device can be used, are described for example in EP2332631 B1.
In an adsorption drying method of this type, an adsorption material, for example a silica gel, is used for adsorption. Adsorption materials of this type are able to pick up and bond, i.e. adsorb, relatively large amounts of water from a gas phase, such as compressed air. Adsorption materials which have adsorbed water can also release, i.e. desorb, said water back to the gas phase. The speed with which adsorption and desorption take place generally depends on the water concentration in the gas phase, on the loading of the adsorption material, i.e. the ratio of bound water mass to the mass of the adsorption material, and on the temperature. When the amounts of water adsorbed and desorbed per unit time are equal in size, and therefore the water concentration in the gas phase and the loading of the adsorption material do not change, this is referred to as adsorption equilibrium. The concentration in the gas phase is then the equilibrium concentration corresponding to the loading, the loading of the adsorption material is the equilibrium loading corresponding to the water concentration. If the loading of the adsorption material is less than the equilibrium loading which occurs at the current temperature and water concentration in the gas phase, the adsorption material can pick up water and thus dry the gas phase. If, however, the loading of the adsorption material is greater than the equilibrium loading, the adsorption material releases water to the gas phase.
The equilibrium loading of the adsorption material at a particular water concentration in the gas phase is lower, the higher the temperature is. Therefore, regeneration can be carried out using adsorption material loaded with water at high temperatures, i.e. the water can be released to the gas phase. As a result, after an intermediate cooling, the adsorption material is able to pick up water from the gas phase again.
In the case of the device described in EP2332631 B1, the adsorption material passes through three different sectors during one rotation. In a drying sector, a cool, moist compressed air flows through the adsorption material, and the adsorption material picks up moisture from said air (adsorption) so that the compressed air is dried. In a subsequent regeneration sector, hot compressed air flows through the adsorption material and warms it. As a result of the warming, the adsorption material releases moisture to the compressed air (desorption). After passing through the regeneration sector, the adsorption material has a low moisture load again and is thus regenerated with respect to moisture for the next pass through the drying sector. However, since the adsorption material is still hot after this regeneration, it is firstly moved through a cooling sector after the regeneration, in that dried, cool compressed air flows through said material and cools it. In the drying sector, the dry and cool adsorption material can then pick up moisture from the compressed air to be dried again.
It has been found that drying compressed air by means of the above-described adsorption drying device produces good results in particular with low pressure dew points in an output gas flow when the adsorption device is operated in stationary operation with continuous transportation of compressed air.
However, it would be desirable to improve the dehumidification yet further in cases where the adsorption device or a system in which the adsorption device is integrated is operated intermittently or very intermittently. A very intermittent operation of this type comes about for example when the transportation of compressed air, for example due to significant fluctuation in the compressed air requirement, is frequently interrupted and then resumed for relatively short intervals of time, to then be interrupted once again.